Low profile transcatheter heart valve

ABSTRACT

An implantable prosthetic valve, according to one embodiment, comprises a frame, a leaflet structure, and a skirt member. The frame can have a plurality of axial struts interconnected by a plurality of circumferential struts. The leaflet structure comprises a plurality of leaflets (e.g., three leaflets arrange to form a tricuspid valve). The leaflet structure has a scalloped lower edge portion secured to the frame. The skirt member can be disposed between the leaflet structure and the frame.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/059,656, filed Jun. 6, 2008, which is incorporatedherein by reference.

FIELD

The present disclosure relates to implantable devices and, moreparticularly, to valve prosthetics for implantation into body ducts,such as native heart valve annuluses.

DESCRIPTION OF THE RELATED ART

The human heart can suffer from various valvular diseases. Thesevalvular diseases can result in significant malfunctioning of the heartand ultimately require replacement of the native valve with anartificial valve. There are a number of known artificial valves and anumber of known methods of implanting these artificial valves in humans.

Various surgical techniques may be used to repair a diseased or damagedvalve. In a valve replacement operation, the damaged leaflets areexcised and the annulus sculpted to receive a replacement valve. Due toaortic stenosis and other heart valve diseases, thousands of patientsundergo surgery each year wherein the defective native heart valve isreplaced by a prosthetic valve, either bioprosthetic or mechanical.Another less drastic method for treating defective valves is throughrepair or reconstruction, which is typically used on minimally calcifiedvalves. The problem with surgical therapy is the significant insult itimposes on these chronically ill patients with high morbidity andmortality rates associated with surgical repair.

When the valve is replaced, surgical implantation of the prostheticvalve typically requires an open-chest surgery during which the heart isstopped and patient placed on cardiopulmonary bypass (a so-called“heart-lung machine”). In one common surgical procedure, the diseasednative valve leaflets are excised and a prosthetic valve is sutured tothe surrounding tissue at the valve annulus. Because of the traumaassociated with the procedure and the attendant duration ofextracorporeal blood circulation, some patients do not survive thesurgical procedure or die shortly thereafter. It is well known that therisk to the patient increases with the amount of time required onextracorporeal circulation. Due to these risks, a substantial number ofpatients with defective valves are deemed inoperable because theircondition is too frail to withstand the procedure. By some estimates,more than 50% of the subjects suffering from aortic stenosis who areolder than 80 years cannot be operated on for aortic valve replacement.

Because of the drawbacks associated with conventional open-heartsurgery, percutaneous and minimally-invasive surgical approaches aregarnering intense attention. In one technique, a prosthetic valve isconfigured to be implanted in a much less invasive procedure by way ofcatheterization. For instance, U.S. Pat. Nos. 5,411,522 and 6,730,118,which are incorporated herein by reference, describe collapsibletranscatheter heart valves that can be percutaneously introduced in acompressed state on a catheter and expanded in the desired position byballoon inflation or by utilization of a self-expanding frame or stent.

An important design parameter of a transcatheter heart valve is thediameter of the folded or crimped profile. The diameter of the crimpedprofile is important because it directly influences the physician'sability to advance the valve through the femoral artery or vein. Moreparticularly, a smaller profile allows for treatment of a widerpopulation of patients, with enhanced safety.

SUMMARY

The present disclosure is directed toward new and non-obvious methodsand apparatuses relating to prosthetic valves, such as heart valves.

In one representative embodiment, an implantable prosthetic valvecomprises a radially collapsible and expandable frame, or stent, and aleaflet structure comprising a plurality of leaflets. The leafletstructure has a scalloped lower edge portion that is positioned insideof and secured to the frame. The valve can further include an annularskirt member, which can be disposed between the frame and the leafletstructure such that the scalloped lower edge portion can be attached toan inner surface of the skirt member. Each leaflet can have an upperedge, a curved lower edge and two side flaps extending betweenrespective ends of the upper edge and the lower edge, wherein each sideflap is secured to an adjacent side flap of another leaflet to formcommissures of the leaflet structure. Each commissure can be attached toone of the commissure attachment posts, and a reinforcing bar can bepositioned against each side flap for reinforcing the attachmentsbetween the commissures and the commissure attachment posts.

The frame can comprise a plurality of angularly spaced, axial strutsthat are interconnected by a plurality of rows of circumferentialstruts. Each row of circumferential struts desirably includes strutsarranged in a zig-zag or saw-tooth pattern extending around thecircumference of the frame.

In certain embodiments, at least one row, and preferably all rows, ofcircumferential struts include pairs of circumferential struts extendingbetween two axial struts. Each strut of the pair has one end connectedto a respective axial strut and another end interconnected to anadjacent end of the other strut of the same pair by a crown portion suchthat a gap exists between the adjacent ends of the struts. The anglebetween the struts of each pair desirably is between about 90 and 110degrees, with about 100 degrees being a specific example. The framedesirably is made of a nickel-cobalt based alloy, such as a nickelcobalt chromium molybdenum alloy (e.g., MP35N™).

In another representative embodiment, an implantable prosthetic valvecomprises a radially collapsible and expandable annular frame and aleaflet structure supported by the frame. The frame can comprise aplurality of interconnected struts defining a plurality of open cells inthe frame. The valve further includes an annular cover member disposedon and covering the cells of at least a portion of the frame. The covermember desirably comprises an elastomer, such as silicon, that canexpand and stretch when the valve is expanded from a crimped state to anexpanded state.

The cover member may be a thin sleeve of silicon that surrounds at leasta portion of the frame. Alternatively, the cover member may be formed bydipping at least a portion of the frame in silicon or another suitableelastomer in liquefied form.

In another representative embodiment, a method is disclosed for crimpingan implantable prosthetic valve having a frame and leaflets supported bythe frame. The method comprises placing the valve in the crimpingaperture of a crimping device such that a compressible material isdisposed between the crimping jaws of the crimping device and the frameof the valve. Pressure is applied against the compressible material andthe valve with the crimping jaws to radially crimp the valve to asmaller profile and compress the compressible material against the valvesuch that the compressible material extends into open cells of the frameand pushes the leaflets away from the inside of the frame.

The foregoing and other features and advantages of the invention willbecome more apparent from the following detailed description, whichproceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a representative embodiment of aprosthetic heart valve.

FIG. 2 is another perspective view of the prosthetic valve of FIG. 1.

FIG. 3 is another perspective view of the prosthetic valve of FIG. 1.

FIG. 4 is an enlarged view of a section of the valve shown in FIG. 3.

FIG. 5 is a bottom perspective view of the prosthetic valve of FIG. 1showing the inside of the valve.

FIG. 6 is a top plan view of the prosthetic valve of FIG. 1.

FIG. 6A is an enlarged partial top view of the valve of FIG. 1illustrating the positioning of the reinforcing bars with respect to thecommissure attachment posts of the frame.

FIG. 7 is a perspective view of the frame of the prosthetic valve ofFIG. 1.

FIG. 8 is a perspective view of an alternative embodiment of a framethat can be used in the prosthetic valve of FIG. 1.

FIG. 9 is a flattened view of 120-degree segment of the frame shown inFIG. 7.

FIG. 10 is a flattened view of 120-degree segment of the frame shown inFIG. 8.

FIG. 11 is a front view of a reinforcing bar that can be used toreinforce the connection of the valve leaflets to a frame in aprosthetic valve such as shown in FIG. 1.

FIG. 12 is a perspective view of the reinforcing bar of FIG. 11 and aPET sleeve that can be used to cover the bar.

FIG. 13 is a flattened view of a leaflet of the valve shown in FIG. 1.

FIG. 14 is a flattened view of the opposite side of the leaflet showinga reinforcing strip secured adjacent the bottom edge of the leaflet.

FIG. 15 is a top plan view of the leaflet structure of the valve of FIG.1 prior to attachment to the frame.

FIG. 16 is a flattened view of the skirt used in the valve shown in FIG.1.

FIG. 17 is a side view of the skirt illustrating suture lines forattaching the skirt to the leaflet structure.

FIG. 18 is a bottom perspective view of the leaflet structure connectedto the skirt so as to form a leaflet assembly.

FIG. 19 is a side view of a balloon catheter and a prosthetic valvecrimped onto the balloon of the balloon catheter.

FIG. 20 is a front view of a crimping device showing a prosthetic valvepositioned in the crimping aperture of the crimping device with aprotective sleeve disposed between the valve and the crimping jaws.

FIG. 21 is a front view of the crimping device shown after the crimpingjaws are forced inwardly to compress the valve and the protectivesleeve.

FIG. 22 is a side view of the valve and protective sleeve after removalfrom the crimping device.

FIG. 23 is a side view of a prosthetic valve that has been crimped ontoa balloon of a balloon catheter without a protective sleeve.

FIG. 24 is a side view of a prosthetic valve that has been crimped ontoa balloon of a balloon catheter using a protective sleeve in the mannershown in FIGS. 20-21.

FIG. 25 is a side view of a frame for a prosthetic valve having asilicon skirt, or sleeve, disposed on the outside of the frame.

FIG. 26 is a side view of a frame for a prosthetic valve having asilicon encapsulating layer covering the inside and outside of theframe.

FIG. 27 is a perspective view of a prosthetic valve comprising a framehaving a silicon encapsulating layer.

FIG. 28 is a perspective view of the valve of FIG. 27 after it has beencrimped to a smaller diameter.

FIG. 29 is a side view of the valve of FIG. 27 after it has beenexpanded by a balloon catheter.

FIGS. 30A-30C are graphs illustrating the results of respective uniaxialtests performed on respective silicon test strips.

FIGS. 31A-31F are graphs illustrating the results of respective uniaxialtests performed on respective silicon test strips having deliberatelyintroduced tears.

DETAILED DESCRIPTION

FIGS. 1 and 2 illustrate an implantable prosthetic valve 10, accordingto one embodiment. Valve 10 in the illustrated embodiment generallycomprises a frame, or stent, 12, a leaflet structure 14 supported by theframe, and a skirt 16 secured to the outer surface of the leafletstructure. Valve 10 typically is implanted in the annulus of the nativeaortic valve but also can be adapted to be implanted in other nativevalves of the heart or in various other ducts or orifices of the body.Valve 10 has a “lower” end 80 and an “upper” end 82. In the context ofthe present application, the terms “lower” and “upper” are usedinterchangeably with the terms “inflow” and “outflow”, respectively.Thus, for example, the lower end 80 of the valve is its inflow end andthe upper end 82 of the valve is its outflow end.

Valve 10 and frame 12 are configured to be radially collapsible to acollapsed or crimped state for introduction into the body on a deliverycatheter and radially expandable to an expanded state for implanting thevalve at a desired location in the body (e.g., the native aortic valve).Frame 12 can be made of a plastically-expandable material that permitscrimping of the valve to a smaller profile for delivery and expansion ofthe valve using an expansion device such as the balloon of a ballooncatheter. Exemplary plastically-expandable materials that can be used toform the frame are described below. Alternatively, valve 10 can be aso-called self-expanding valve wherein the frame is made of aself-expanding material such as Nitinol. A self-expanding valve can becrimped to a smaller profile and held in the crimped state with arestraining device such as a sheath covering the valve. When the valveis positioned at or near the target site, the restraining device isremoved to allow the valve to self-expand to its expanded, functionalsize.

Referring also to FIG. 7 (which shows the frame alone for purposes ofillustration), frame 12 is an annular, stent-like structure having aplurality of angularly spaced, vertically extending, commissureattachment posts, or struts, 18. Posts 18 can be interconnected via alower row 36 a of circumferentially extending struts 20 and first andsecond rows upper rows 36 b, 36 c, respectively, of circumferentiallyextending struts 22 and 24, respectively. The struts in each rowdesirably are arranged in a zig-zag or generally saw-tooth like patternextending in the direction of the circumference of the frame as shown.Adjacent struts in the same row can be interconnected to one another asshown in FIGS. 1 and 5 to form an angle A, which desirably is betweenabout 90 and 110 degrees, with about 100 degrees being a specificexample. The selection of angle A between approximately 90 and 110degrees optimizes the radial strength of frame 12 when expanded yetstill permits the frame 12 to be evenly crimped and then expanded in themanner described below.

In the illustrated embodiment, pairs of adjacent circumferential strutsin the same row are connected to each other by a respective, generallyU-shaped crown structure, or crown portion, 26. Crown structures 26 eachinclude a horizontal portion extending between and connecting theadjacent ends of the struts such that a gap 28 is defined between theadjacent ends and the crown structure connects the adjacent ends at alocation offset from the strut's natural point of intersection. Crownstructures 26 significantly reduce residual strains on the frame 12 atthe location of struts 20, 22, 24 during crimping and expanding of theframe 20 in the manner described below. Each pair of struts 22 connectedat a common crown structure 26 forms a cell with an adjacent pair ofstruts 24 in the row above. Each cell can be connected to an adjacentcell at a node 32. Each node 32 can be interconnected with the lower rowof struts by a respective vertical (axial) strut 30 that is connected toand extends between a respective node 32 and a location on the lower rowof struts 20 where two struts are connected at their ends opposite crownstructures 26.

In certain embodiments, lower struts 20 have a greater thickness ordiameter than upper struts 22, 24. In one implementation, for example,lower struts 20 have a thickness T (FIG. 9) of about 0.42 mm and upperstruts 22, 24 have a thickness T of about 0.38 mm. Because there is onlyone row of lower struts 20 and two rows of upper struts 22, 24 in theillustrated configuration, enlargement of lower struts 20 with respectto upper struts 22, 24 enhances the radial strength of the frame at thelower area of the frame and allows for more uniform expansion of theframe.

FIG. 9 shows a flattened view of a 120-degree segment of frame 12 shownin FIG. 7, the segment comprising a portion of the frame extendingbetween two posts 18. As shown, the frame segment has three columns 34and three rows 36 a, 36 b, 36 c of struts per segment. Each column 34 isdefined by the adjoining pairs of struts 20, 22, 24 extending betweentwo axially extending struts 18, 30. Frame 12 desirably is comprised ofthree 120-degree segments, with each segment being bounded by two posts18. Accordingly, frame 12 in the illustrated embodiment includes 9 totalcolumns per frame.

The number of columns and rows desirably is minimized to reduce theoverall crimp profile of the valve, as further discussed below. Thearrangement of FIGS. 7 and 9 typically is used for valves that are lessthan about 29 mm in diameter, and are most suitable for valves that areabout 20-26 mm in diameter. In working examples of valves comprisingframe 12, a 20-mm valve can be crimped to a diameter of about 17 Fr, a23-mm valve can be crimped to a diameter of about 18 Fr and a 26-mmvalve can be crimped to a diameter of about 19 Fr. For valves that areabout 29 mm and larger in diameter, it may be desirable to add anotherrow and column of struts.

For example, FIGS. 8 and 10 show an alternative frame 40 that is similarto frame 12 except that frame 40 has four rows of struts (a lowermost,first row 52 a of struts 42, a second row 52 b of struts 44, a third row52 c of struts 46, and an uppermost row 52 d of struts 48) instead ofthree rows of struts, as well as four columns 50 of struts for each120-degree frame segment instead of three columns of struts. FIG. 10shows a flattened view of a 120-degree segment of frame 40 shown in FIG.8. Frame 40 in the illustrated embodiment includes three such 120-degreesegments, providing 12 total columns 50 of struts for the frame.

Struts 46 of the third row desirably are facing in the oppositedirection of the struts 48 of the fourth row (i.e., the apexes or crownportions are facing in the opposite direction), to help avoid bucklingof the vertical posts of the frame during crimping and expansion of thevalve. Struts 44 of the second row can be arranged so as to be facing inthe same direction as the struts 42 of the first row as shown (i.e., theapexes or crown portions are facing in the same direction).Alternatively, struts 44 of the second row can be facing in the opposingdirection from struts 42 of the first row so as to form square cells,like the cells formed by the struts 46, 48 of the third and fourth rows,respectively. Frame 40 can also include axially extending struts 54connected to and extending between the ends of each strut 42, 44, 46,and 48 aligned in a column 50 that are not connected to a post 18. Asnoted above, frame 40 is most suitable for valves 29 mm and larger indiameter (when expanded to its functional size). In a working example ofa valve incorporating frame 40, a 29-mm valve can be crimped to adiameter of about 21 Fr.

Suitable plastically-expandable materials that can be used to form theframe include, without limitation, stainless steel, a nickel based alloy(e.g., a nickel-cobalt-chromium alloy), polymers, or combinationsthereof. In particular embodiments, frame 20 is made of anickel-cobalt-chromium-molybdenum alloy, such as MP35N™ (tradename ofSPS Technologies), which is equivalent to UNS R30035 (covered by ASTMF562-02). MP35N™/UNS R30035 comprises 35% nickel, 35% cobalt, 20%chromium, and 10% molybdenum, by weight. It has been found that the useof MP35N to form frame 20 provides superior structural results overstainless steel. In particular, when MP35N is used as the framematerial, less material is needed to achieve the same or betterperformance in radial and crush force resistance, fatigue resistances,and corrosion resistance. Moreover, since less material is required, thecrimped profile of the frame can be reduced, thereby providing a lowerprofile valve assembly for percutaneous delivery to the treatmentlocation in the body.

Referring again to FIG. 1, skirt 16 can be formed, for example, ofpolyethylene terephthalate (PET) ribbon. The thickness of the skirt canvary, but is desirably less than 6 mil, and desirably less than 4 mil,and even more desirably about 2 mil. Skirt 16 can be secured to theinside of frame 12 via Lenzing sutures 56, as shown in FIG. 1. Leafletstructure 14 can be attached to the skirt via a thin PET reinforcingstrip 68 (or sleeve), discussed below, which enables a secure suturingand protects the pericardial tissue of the leaflet structure from tears.Leaflet structure 14 can be sandwiched between skirt 16 and the thin PETstrip 68 as shown. Suture 58, which secures the PET strip and theleaflet structure 14 to skirt 16 can be any suitable suture, such as anEthibond suture. Suture 58 desirably tracks the curvature of the bottomedge of leaflet structure 14, as described in more detail below. Leafletstructure 14 can be formed of bovine pericardial tissue, biocompatiblesynthetic materials, or various other suitable natural or syntheticmaterials as known in the art and described in U.S. Pat. No. 6,730,118,which is incorporated by reference herein.

Leaflet structure 14 can comprise three leaflets 60, which can bearranged to collapse in a tricuspid arrangement, as best shown in FIGS.2 and 6. The lower edge of leaflet structure 14 desirably has anundulating, curved scalloped shape (suture line 58 shown in FIG. 1tracks the scalloped shape of the leaflet structure). By forming theleaflets with this scalloped geometry, stresses on the leaflets arereduced, which in turn improves durability of the valve. Moreover, byvirtue of the scalloped shape, folds and ripples at the belly of eachleaflet (the central region of each leaflet), which can cause earlycalcification in those areas, can be eliminated or at least minimized.The scalloped geometry also reduces the amount of tissue material usedto form leaflet structure, thereby allowing a smaller, more even crimpedprofile at the inflow end of the valve.

Leaflets 60 can be secured to one another at their adjacent sides toform commissures 84 of the leaflet structure (the edges where theleaflets come together). Leaflet structure 14 can be secured to frame 12using suitable techniques and mechanisms. For example, as best shown inFIG. 6, commissures 84 of the leaflet structure desirably are alignedwith the support posts 18 and secured thereto using sutures. The pointof attachment of the leaflets to the posts 18 can be reinforced withbars 62 (FIG. 11), which desirably are made of a relatively rigidmaterial (compared to the leaflets), such as stainless steel.

FIG. 13 shows a single leaflet 60, which has a curved lower edge 64 andtwo flaps 66 extending between the upper edge and curved lower edge ofthe leaflet. The curved lower edge 64 forms a single scallop. Whensecured to two other leaflets to form leaflet structure 14, the curvedlower edges of the leaflets collectively form the scalloped shaped loweredge portion of the leaflet structure (as best shown in FIG. 18). Asfurther shown in FIG. 13, two reinforcing bars 62 can be secured to theleaflet adjacent to flaps 66 (e.g., using sutures). The flaps can thenbe folded over bars 62 and secured in the folded position using sutures.If desired, as shown in FIG. 12, each bar 62 can be placed in aprotective sleeve 68 (e.g., a PET sleeve) before being secured to aleaflet.

As shown in FIG. 14, the lower curved edge 64 of the leaflet can bereinforced for later securement to the skirt 16, such as by securing areinforcing strip 68 along the curved lower edge between flaps 66 on theside of the leaflet opposite bars 62. Three such leaflets 60 can beprepared in the same manner and then connected to each other at theirflaps 66 in a tricuspid arrangement to form leaflet structure 14, asshown in FIG. 15. The reinforcing strips 68 on the leaflets collectivelydefine a ribbon or sleeve that extends along the lower edge portion ofthe inside surface of the leaflet structure.

As noted above, leaflet structure 14 can be secured to frame 12 withskirt 16. Skirt 16 desirably comprises a tough, tear resistant materialsuch as PET, although various other synthetic or natural materials canbe used. Skirt 16 can be much thinner than traditional skirts. In oneembodiment, for example, skirt 16 is a PET skirt having a thickness ofabout 0.07 mm at its edges and about 0.06 mm at its center. The thinnerskirt can provide for better crimping performances while still providinggood perivalvular sealing.

FIG. 16 shows a flattened view of the skirt before the opposite ends aresecured to each other to form the annular shape shown in FIG. 17. Asshown, the upper edge of skirt 16 desirably has an undulated shape thatgenerally follows the shape of the second row of struts 22 of the frame.In this manner, the upper edge of skirt 16 can be tightly secured tostruts 22 with sutures 56 (as best shown in FIG. 1). Skirt 16 can alsobe formed with slits 70 to facilitate attachment of the skirt to theframe. Slits 70 are aligned with crown structures 26 of struts 22 whenthe skirt is secured to the frame. Slits 70 are dimensioned so as toallow an upper edge portion of skirt to be partially wrapped aroundstruts 22 and reduce stresses in the skirt during the attachmentprocedure. For example, in the illustrated embodiment, skirt 16 isplaced on the inside of frame 12 and an upper edge portion of the skirtis wrapped around the upper surfaces of struts 22 and secured in placewith sutures 56. Wrapping the upper edge portion of the skirt aroundstruts 22 in this manner provides for a stronger and more durableattachment of the skirt to the frame. Although not shown, the lower edgeof the skirt can be shaped to conform generally to the contour of thelowermost row of struts 22 to improve the flow of blood past the inflowend of the valve.

As further shown in FIG. 17, various suture lines can be added to theskirt to facilitate attachment of the skirt to the leaflet structure andto the frame. For example, a scalloped shaped suture line 72 can be usedas a guide to suture the lower edge of the leaflet structure at theproper location against the inner surface of the skirt using suture 59(as best shown in FIG. 5). Another scalloped shaped suture line 74 (FIG.17) can be use as a guide to suture the leaflet structure to the skirtusing sutures 58 (FIG. 1). Reinforcing strips 68 secured to the loweredge of the leaflets reinforces the leaflets along suture line 58 andprotects against tearing of the leaflets. FIG. 18 shows a leafletassembly comprised of skirt 16 and leaflet structure 14 secured to theskirt. The leaflet assembly can then be secured to frame 12 in themanner described below. In alternative embodiments, the skirt, withoutthe leaflet structure, can be connected to the frame first, and then theleaflet structure can be connected to the skirt.

FIG. 6 shows a top view of the valve assembly attached to frame 12.Leaflets 60 are shown in a generally closed position. As shown, thecommissures of the leaflets are aligned with posts 18 of the frame. Theleaflets can be secured to the frame using sutures extending throughflaps 66 of the leaflets, openings 76 in bars 62, and openings 78 inposts 18, effectively securing flaps 66 to posts 18. As noted above,bars 62 reinforce the flaps at the area of connection with posts andprotect against tearing of the leaflets.

As shown in FIG. 6A, bars 62 desirably are aligned perpendicular and asstraight as possible with respect to posts 18 of the frame, such thatbars 62 and post 18 at each commissure form a “T” shape. The width ofbars 62 and the attachment of the commissures via the bars provides aclearance between the deflectable portions of the leaflets 60 (theportions not secured by sutures to the frame) and the frame, while theedge radius (thickness) of bars 62 serves as a flex hinge for theleaflets 60 during valve opening and closing, thereby increasing thespace between the leaflets and the frame. By increasing the spacebetween the moving portions of the leaflets and frame and by having theleaflets flex against an edge radius of bars 62, contact between themoving portions of the leaflets (especially the outflow edges of theleaflets) and the frame can be avoided during working cycles, which inturn improves the durability of the valve assembly. This configurationalso enhances perfusion through the coronary sinuses.

FIG. 19 depicts a side view of a valve 10 crimped on a balloon deliverycatheter 100. The valve is crimped onto balloon 110 of balloon catheter100. It is desirable to protect leaflet structure 14 of the valve fromdamage during crimping to ensure durability of the leaflet structure andat the same time, it is desirable to reduce as much as possible thecrimped profile size of the valve. During the crimping procedure thetissue of the leaflet structure (e.g., bovine pericardial tissue orother suitable tissue) is pressed against the inner surface of the metalframe and portions of the tissue can protrude into the open cells of theframe between the struts and can be pinched due to the scissor-likemotion of the struts of the frame. If the valve is severely crimped toachieve a small crimping size, this scissor-like motion can result incuts and rupture of the tissue leaflets.

Skirt 16, described above, can protect against damage to the leafletstructure during crimping to a certain degree. However, the skirt's mainpurpose is structural and it does not in certain embodiments cover theentire frame. Therefore, in such embodiments, the skirt may not fullyprotect the leaflet structure during crimping and as such, the frame canstill cause damage to the leaflet structure.

FIGS. 20 and 21 show an embodiment of a crimping apparatus foratraumatic crimping of a valve onto a balloon in a manner that furtherprotects against damage to the leaflets. The crimping apparatus (alsoreferred to as a crimper), indicated generally at 200, has an aperture202 sized to receive a valve in an expanded state. FIG. 20 showsaperture 202 in a fully open or dilated state with a valve 10 positionedinside aperture 202. Crimping apparatus 200 has a plurality of crimperjaws 206 (12 in the illustrated embodiment) which are configured to moveradially inwardly to radially compress (crimp) the valve to a smallerprofile around the balloon of a balloon catheter.

A deformable material is positioned between the outside of the frame andthe crimping jaws 206. In the illustrated embodiment, the deformablematerial comprises a protective sleeve, or covering, 204 that is placedaround the valve so that it covers the outer surface of the frame of thevalve and prevents the hard surface of the crimping jaws from directlycontacting the frame of the valve. The sleeve 204 desirably is sized tofully cover the outer surface of the frame. Sleeve 204 desirably is madeof a soft, flexible and compressible material. The sleeve can be formedfrom generally available materials, including, but not limited to,natural or synthetic sponge (e.g., polyurethane sponge), a foamedmaterial made of a suitable polymer such as polyurethane orpolyethylene, or any of various suitable elastomeric materials, such aspolyurethane, silicon, polyolefins or a variety of hydrogels, to name afew.

The sleeve is desirably stored in a wet environment (e.g., immersed insaline) prior to use. After placing sleeve 204 around the valve, thevalve and the sleeve are placed into crimping apparatus 200 as shown inFIG. 20. Balloon 110 of a balloon catheter can then be positioned withinthe leaflets 60 of the valve (FIG. 21). FIG. 21 shows crimper jaws 206surrounding sleeve 204, which in turn surrounds frame 12 and leafletstructure 14 of valve 10. Balloon 110 typically is placed at the centerof the valve so that the valve can be evenly expanded duringimplantation of the valve within the body.

As seen in FIG. 21, during crimping, the sponge-like material ofprotective sleeve 204 protrudes into the open cells of frame 12 andoccupies this space, thereby preventing leaflet structure 14 fromentering this space and being pinched or otherwise damaged. Aftercrimping is completed, the valve with the protective sleeve is removedfrom the crimping apparatus. Sleeve 204 can then be gently peeled awayfrom the frame. Because the protective sleeve presses the leafletstructure inwardly and away from the frame during crimping, the valvecan be crimped to a small profile without damaging the leafletstructure.

FIGS. 23 and 24 illustrate an advantage that can be gained by usingprotective sleeve 204. FIG. 23 shows a prosthetic valve that was crimpedwithout using the protective sleeve. Dotted line 300 identifies an areaof the valve where leaflet structure 302 has been pressed between strutsof a frame 304, which can damage the leaflet structure as discussedabove.

In contrast, FIG. 24 shows a prosthetic valve that was crimped usingprotective sleeve 204. In this example, leaflet structure 302 waspressed inwardly and away from the inside of frame 304 and, therefore,the leaflet structure was not pinched or squeezed between the struts ofthe frame.

Accordingly, since the leaflet structure is pushed away from the framewhen the protective sleeve is used, the leaflet structure is less likelyto be pinched or cut during the crimping process. Also, when using aprotective sleeve, a very ordered structure of balloon-leaflets-frame(from inward to outward) can be achieved. When no such protective sleeveis utilized, some portion of the balloon, leaflets, and frame are muchmore likely to overlap after the crimping procedure and the resultingstructure is less predictable and uniform.

In addition to the foam or sponge-type protective sleeve describedabove, other types of sleeves or protective layers of deformablematerial can be used to protect the leaflets against damage duringcrimping of a valve. In one implementation, for example, a layer (e.g.,rectangular slices) of deformable material (e.g., sponge, rubber,silicon, polyurethane, etc.) can be disposed on each crimping jaw 206 soas to form a sleeve around the valve upon crimping. Alternatively,deformable packets filled with a flowable, deformable material, such asa gel or gas, can be disposed on each crimping jaw for contacting thevalve upon crimping. In addition, the deformable material (e.g., sleeve204) can be covered with a thin PET cloth, among many other fabricmaterials or other suitable materials, to prevent particles of thedeformable materials from migrating to the valve during crimping.

The skirt of a prosthetic valve serves several functions. In particularembodiments, for example, the skirt functions to seal and prevent (ordecrease) perivalvular leakage, to anchor the leaflet structure to theframe, and to protect the leaflets against damage caused by contact withthe frame during crimping and during working cycles of the valve. Theskirt used with the prosthetic valve discussed above has been describedas being a fabric, such as a PET cloth. PET or other fabrics aresubstantially non-elastic (i.e., substantially non-stretchable andnon-compressible). As such, the skirt in certain implementations limitsthe smallest achievable crimping diameter of the valve and can wrinkleafter expansion from the crimped diameter.

In alternative embodiments, such as discussed below, a prosthetic valvecan be provided with a skirt that is made of a stretchable and/orcompressible material, such as silicon. Due to the compressibility ofsuch a skirt, the valve can be crimped to a relatively smaller diameteras compared to a valve having a non-compressible skirt. Furthermore,such a skirt can recover its original, smooth surfaces with little or nowrinkling after expansion from the crimped state.

FIG. 25 shows an embodiment of a frame 12 that has an elastic“over-tube” skirt or sleeve 340 that extends completely around andcovers at least a portion of the outside of the frame. In particularembodiments, skirt 340 is made of silicon, which can undergo largedeformations while maintaining its elasticity. Such a silicon skirt canbe a thin sleeve that covers a portion of frame 12 from the outside. Inthe illustrated embodiment, the height of the skirt is less than theoverall height of frame 12, however, the skirt can vary in height andneed not be the height shown in FIG. 25. For example, the height of theskirt can be the same as or greater than that of the frame so as tocompletely cover the outside of the frame. In an alternative embodiment,the skirt 340 can be mounted to the inside of the frame using, forexample, sutures or an adhesive. When mounted inside of the frame, theskirt can protect the leaflets from abrasion against the inside of theframe. Other materials that can be used to form the skirt or sleeveinclude, but are not limited to, PTFE, ePTFE, polyurethane, polyolefins,hydrogels, biological materials (e.g., pericardium or biologicalpolymers such as collagen, gelatin, or hyaluronic acid derivatives) orcombinations thereof.

In another embodiment, the entire frame or a portion thereof can bedipped in liquefied material (e.g., liquid silicon or any of thematerials described above for forming the sleeve 340 that can beliquefied for dip coating the frame) in order to encapsulate the entireframe (or at least that portion that is dipped) in silicon. FIG. 26 is aside view of a frame 12 that has been dipped in silicon to form acontinuous cylindrical silicon covering 342 encapsulating the struts ofthe frame and filling the spaces between the struts. FIG. 26 shows thecovering 342 before it is trimmed to remove excess material extendingbeyond the ends of the frame. Although less desirable, the frame can bedipped such that the silicon encapsulates the struts of the frame butdoes not fill the open spaces between the struts of the frame.

FIG. 27 shows an embodiment of a prosthetic valve 400 comprising a frame402 and a leaflet structure 404 mounted to the inside of the frame(e.g., using sutures as shown). Frame 402 has a skirt in the form ofsilicon covering 406 that is formed, for example, by dipping the frameinto liquid silicon. FIG. 27 shows valve 400 in its expanded state. InFIG. 28, valve 400 has been crimped to a smaller profile. Duringcrimping, coating 406, which extends across and fills the open cellsbetween the struts of the frame, is effective to push leaflet structure404 inward and away from the frame, thereby protecting the leafletstructure from pinching or tearing. FIG. 29 shows valve 400 after beingexpanded by a balloon of a balloon catheter.

In order to test the durability and stretch resistance of the siliconused, several uniaxial tests were conducted. In particular, siliconstrips of about 5×50 mm (with a thickness of about 0.85 mm) were testedin a uniaxial tester. FIGS. 30A-30C show graphs of the results of theuniaxial testing of silicon strips. In addition, tears were deliberatelyintroduced into silicon strips at a middle of the strips and at the edgeof the strips while the strips were stretched on a uniaxial tester. Thetears were introduced by making holes in the silicon strips with aneedle. FIGS. 31A-31F show graphs of the results of the uniaxial testingof silicon strips with deliberately introduced tears.

It was found that ultimate tensile stretch for a thin layer of siliconwas over 500% and that samples that had tears that were deliberatelyintroduced continued to show notable strength. Accordingly, theelasticity of silicon permits silicon dipped frames to be crimped tovery low profiles and expanded back out to larger profiles withoutsignificant damage to the silicon layer. In addition, the siliconmaterial can increase friction between the frame and the native annuluswhere the prosthetic valve is implanted, resulting in better anchoringand preventing/reducing perivalvular leaks.

A silicon skirt can be mounted on a frame by various means, including byusing a mandrel. Also, it may be desirable to use a silicon skirt incombination with a cloth or fabric skirt. For example, it may bedesirable to place a silicon skirt on the outside of a cloth or fabricskirt that is surrounding at least a portion of a frame.

Alternatively or additionally, a silicon skirt could also be placed onthe inside of the frame and attached to the frame so that it offers theleaflets improved protecting during working cycles. Alternatively,instead of silicon, the skirt can be made of an auxetic and/or swellingmaterial, such as synthetic or natural hydrogels. An auxetic material isone that expands laterally while stretched longitudinally, which meansthat this material has a negative Poisson ration. If the frame iscovered with an auxetic material it can expand radially while beingstretched circumferentially when the valve is expanded from its crimpedstate. Such expansion can improve the fit of the valve at the nativevalve annulus, thereby preventing or reducing perivalvular leakage.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

1. An implantable prosthetic valve comprising: a radially collapsibleand expandable annular frame, the frame having a plurality of angularlyspaced commissure attachment posts; an annular skirt member positionedinside of and secured to the frame; and a leaflet structure comprising aplurality of leaflets, the leaflet structure having a scalloped loweredge portion secured to an inner surface of the skirt member, eachleaflet having an upper edge, a curved lower edge and two side flapsextending between respective ends of the upper edge and the lower edge,wherein each side flap is secured to an adjacent side flap of anotherleaflet to form commissures of the leaflet structure, each commissurebeing attached to one of the commissure attachment posts; and areinforcing bar positioned against each side flap for reinforcing theattachments between the commissures and the commissure attachment posts;wherein the frame comprises a plurality of axial struts and a pluralityof rows of circumferential struts extending between and interconnectingthe axial struts; wherein the rows of circumferential struts includes atleast a first row of circumferential struts adjacent the inflow end ofthe valve and a second row of circumferential struts adjacent theoutflow end of the valve, wherein the struts of the first row arethicker than the struts of the second row.
 2. The prosthetic valve ofclaim 1, wherein the commissures are attached to the commissureattachment posts with sutures extending through the side flaps, thereinforcing bars and the commissure attachment posts.
 3. The prostheticvalve of claim 1, further comprising an elastomeric sleeve disposed onthe outside of the frame.
 4. The prosthetic valve of claim 1, furthercomprising an annular elastomeric layer encapsulating at least a portionof the frame.
 5. The valve of claim 1, wherein at least one row ofcircumferential struts includes pairs of circumferential strutsextending between two axial struts, the struts of each pair havingadjacent ends interconnected by a generally U-shaped crown portiondefining a gap between the adjacent ends.
 6. The valve of claim 5,wherein an angle between each pair of struts is between about 90 and 110degrees.
 7. The valve of claim 1, wherein the frame comprises a nickelcobalt chromium alloy.
 8. The valve of claim 7, wherein the nickelcobalt chromium alloy comprises MP35N.
 9. The valve of claim 1, whereineach leaflet has a curved lower edge portion comprising a scallopextending between two commissures, the curved lower edge portions of theleaflets collectively defining the scalloped lower edge portion of theleaflet structure.
 10. The valve of claim 9, wherein the lower edgeportion of the leaflet structure is secured to the inside of the skirtmember.
 11. The valve of claim 10, further comprising a reinforcingstrip, separate from the skirt member, that is secured to an innersurface of the lower edge portion of the leaflet structure.